The invention relates to installations for continuously treating a strip product such as a film, web, cloth, or other fiber or non-fiber thin substrate.
A particular field of application of the invention is continuously treating strip products in a furnace in order to form a deposit thereon, to perform surface treatment thereon, or to perform carbonization thereof. The invention relates particularly, but not exclusively, to continuously carbonizing fiber substrates such as cloth or web made of fiber or yarn.
Installations are known for producing carbon fiber cloth by continuously carbonizing cloth made of carbon-precursor fibers. Reference can be made in particular to Russian patent No. RU 2 005 829.
The cloth to be carbonized, e.g. made of cellulose fibers, travels continuously through a furnace in which the carbon precursor is transformed by pyrolysis so that a carbon fiber cloth is recovered continuously from the outlet of the furnace.
Pyrolysis is performed under an inert atmosphere by injecting a gas, e.g. nitrogen, into inlet and outlet zones at the ends of the furnace. The inert gas is extracted together with the effluent of the pyrolysis via chimneys leading away from various zones of the furnace.
The inside of the furnace must be sealed so as to be sure that no pyrolysis effluent can escape to the outside through the inlet or the outlet of the furnace and so as to ensure that no air can penetrate into the inside of the furnace. Effluent escaping from the inlet or the outlet of the furnace would not only make it more difficult to eliminate the effluent, but would also pollute the cloth by allowing tars conveyed by the effluent to condense or deposit thereon. Air penetrating into the furnace would oxidize the cloth and, by cooling the product could also give rise to undesirable condensation of pyrolysis effluent.
Good sealing can be provided by pressing a lip or a roller against the cloth. Nevertheless that can sometimes lead to high levels of friction, thereby inducing tension in the cloth. However, during carbonization, the cloth can shrink considerably. It can shrink substantially freely in the weft direction, but tension applied by friction, e.g. using rollers, prevents shrinkage from taking place freely in the warp direction. This results in excessive weft deformation in the resulting cloth.
Good sealing can also be provided by a dynamic seal formed by a flow of inert gas, such as a nitrogen seal. Nevertheless, that would disturb the aerodynamics inside the furnace and would also cool the pyrolysis effluent, thereby leading to the above-mentioned drawbacks. In addition, such a solution is unsuitable when particular pressure conditions need to be maintained inside the furnace.
An object of the invention is to remedy those drawbacks, and more generally, to provide a sealing box for an enclosure for continuously treating a strip product while providing excellent sealing:
without disturbing the internal aerodynamics of the enclosure;
while maintaining the inside of the enclosure at a desired pressure; and
without exerting tension on the strip product that could lead to its behavior or its appearance being disturbed.
According to the invention, this object is achieved by a sealing box comprising:
a longitudinal passage opening out from the box via a first end for connection to an inlet or an outlet of the enclosure, and via a second end, opposite from the first;
a support surface inside the passage, on which a strip product can travel between the ends of the box; and
static sealing means acting by coming into contact with the strip product travelling along the passage on the support surface;
in which box, according to the invention:
the static sealing means comprise at least one inflatable gasket placed across the passage, above the support surface; and
dynamic sealing means are also provided in the passage between the second end of the box and the static sealing means, the dynamic sealing means comprising means for injecting gas into at least one chamber formed in the passage.
The combination of static sealing means and of dynamic sealing means makes it possible to use static sealing means that exert minimum friction force on the travelling strip product. Thus, the inflatable gasket is preferably inflated to a pressure that exceeds atmospheric pressure by less than 500 Pascals (Pa). It is also made of a material over which the thin products can slide with a minimum amount of friction, e.g. a silicone-coated cloth.
Thus, with a sealing box of the invention, it is possible to limit the tension exerted on the travelling strip product. For a strip product in the form of a cloth that is subjected to carbonization inside the enclosure, the difference between the substantially free shrinkage in the weft direction (expressed as a percentage) and the shrinkage in the warp direction (also expressed in percentage) can be restricted to a value of less than 5%.
The dynamic sealing means advantageously comprise means for injecting gas into a chamber defined by the inflatable gasket and a wall extending across the passage. The dynamic sealing means preferably comprise a plurality of adjacent chambers separated from one another by walls extending across the passage, each chamber being provided with its own gas injection or extraction opening. In this configuration, an extraction chamber is situated between two injection chambers.
Advantageously, the or each wall defining a chamber is provided with a flexible bib at its end adjacent to the path of cloth along the passage, e.g. a bib of silicone-coated cloth. The bib does not perform a static sealing function, and as a result it does not exert any significant force on the strip product travelling along the passage.
According to a feature of the invention, the inflatable flexible gasket is made up of a plurality of adjacent sections aligned side-by-side across the passage, each section being provided with its own inflation means so as to make it possible to adjust the inflation pressure in each section of the gasket independently.
As a result, it is possible to exert a force that varies in the transverse direction on the strip product. When the strip product is cloth that is being subjected to carbonization, that makes it possible to control straightness of grain by compensating for the cloth shifting out of register during carbonization, i.e. for the deformation to which the cloth is subject by weft curvature.